This invention relates to a manually activated flush bolt mechanism for latching the inactive door of a paired swinging doors. Flush bolts, automatically activated or manually activated, are commonly used to latch the inactive door. Two flush bolts are required to latch the inactive door: one at the top thereof, and one at the bottom. The retracted bolts of these mechanisms are usually flush with the respective horizontal top and horizontal bottom edges of the inactive door. Regardless whether the bolts are retracted or projected, these flush bolt mechanisms are also flush with the vertical edge of the inactive door, so that the active door can be closed. When the bolt mechanism is activated, the projected bolt at the horizontal top edge of the inactive door engages with a strike plate located at the door frame above the inactive door. Similarly, when a bolt mechanism is activated, the projected bolt at the horizontal bottom edge of the inactive door engages with a strike plate located at the floor or sill. When an inactive door has to be closed, the flush bolts' triggers have to be first activated, causing the bolts to project into their respective strike plates hence securing the inactive door in a locked position. When an inactive door has to be opened, the flush bolts' triggers have to be first reversibly activated, causing the bolts to retracted out of their respective strike plates thereby allowing the inactive door free to be opened.
The history of prior art reveals a number of flush bolt mechanisms which were designed to be mounted onto the vertical edge of an inactive door of a paired unit. The prior known flush bolt mechanisms can be classified into two broad categories: automatically-activated flush bolts (for instances, U.S. Pat. Nos. 3,578,369, 4,005,886 and 4,099,753), and manually-activated flush bolts (for examples, U.S. Pat. Nos. 1,162,945, 2,819,107, and 4,315,647). Both categories of flush bolts feature some generally recognizable parts: a unitary housing which holds all inner parts, a trigger member, a shaft, a spring (or another means) for biasing the shaft, and a slidable bolt to be projected into and engaged with a strike plate. In the first category as illustrated by the U.S. Pat. No. 4,099,753, the closing active door activates the trigger which then moves the shaft vertically to project a bolt into a strike plate latching the inactive door. In the second category as shown by the example of U.S. Pat. No. 4,315,647, the trigger has to be manually pulled to move the shaft which is connected at one end to the bolt, projecting the bolt into a strike plate. The bolt mechanisms referenced hereby have exhibited in various designs and shapes with one or multiple desirable characteristics. It is desired that the bolt mechanisms can endure heavy usage. It is also desired that the bolt mechanisms can be reliably projected thereby securing the inactive door in a locking position in case of any potential break-in by burglars. Furthermore, it is also desired that the bolts mechanism can be reliably retracted thereby freeing the inactive door to be opened in case of any fire or emergency exit. Finally, the bolt mechanisms have to withstand any extreme heat or cold. Therefore, the bolt mechanisms have to be made sturdy with sufficient activation of the mechanisms and sufficient projection and retraction of the bolts.
Flush bolt mechanisms of prior art are too bulky or too difficult to be mounted onto the vertical edge of an inactive door of a paired unit. They often require multiple routings or cuttings on the vertical edge of the inactive door to achieve the desirable width, length, and depth to accommodate the bolt mechanisms. This invention is better than the prior known bolt mechanisms because it has a simpler design, fewer parts, and a more uniform height. This invention features a heavy-duty flush bolt mechanism which has a strong housing, a solid bolt, a sturdy shaft, and an easily accessible trigger. It offers a reliable projection of the bolt which is the vertical edge of the inactive door 36. The diameter of the screw-holes 13, 14 in the housing is slightly bigger than the Phillips screw heads' diameter, allowing the screws to fit into screw-holes, hence the bolt mechanism is flush with the vertical edge of the inactive door.
The purpose of the strike plate 24 is to receive and engage with the projected bolt for securing the inactive door. Referring to FIG. 6, the strike plate 24 is in general rectangular, and has round corners. It is die-cut from a flat sheet metal. An elliptical opening is at the center of the strike plate, with the long elliptical axis (X-axis) stretching across the length of the strike plate. At the outer edges of the strike plates, there are two identical-sized screw-holes, where two Phillips flat-headed screws 25, 26 are fastening the strike plate onto the door frame 35 (as shown in FIG. 2). The purpose of having an elliptical opening, instead of a circular opening, at the center of the strike plate is to minimize any possible misalignment between the strike plate and the projected bolt.